1. Field of the Invention
The present disclosure relates to an autofocus method for automatically focusing a subject image to be photographed to an appropriate focus position when a focus adjustment is performed in an imaging device such as a video camera or a still camera.
2. Description of the Related Art
Unexamined Japanese Patent Publication No. 1107-15648 discloses a video camera having an autofocus function that is capable of varying a driving speed of a focus motor according to an F-number of a lens barrel. In a situation in which a depth of field is deep due to a small aperture, this video camera increases the driving speed of the focus motor to increase a lens displacement per unit time so that a variation in a focus evaluation value becomes large to prevent a malfunction. On the contrary, in a situation in which the depth of field is shallow due to a large aperture, the video camera decreases the driving speed to decrease the lens displacement per unit time so that the lens is prevented from overshooting in the vicinity of a focus point.
The present disclosure provides an autofocus method that allows an imaging element driver to be driven at an appropriate speed during an autofocus operation, and an autofocus device and an imaging device that use the method.